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Most important part is the function notation: http://en.wikipedia.org/wiki/Function_(mathematics). f(x)=~ is a way of saying a function, similar to y=~. So here, f(2) would mean put a 2 wherever you saw x before. Doing so would give f(2) = -(2)2+(2)+5 = -4+2+5 = 3

[f(a+h)-f(a)]/h is just using this function at 2 points (a and a+h) and dividing by h.

Which can be simplified down to the final answer. (If the above looks like code google texify or get the sidebar plugin).

You can see that every time I substitute in a value, I put it in brackets: (~) This isn't necessary, but it's a good practice to keep correct signs (+-), and make sure all the subbed in stuff gets operated on properly.

Thanks! That was very helpful. I tried to simplify the equation and got to the point (-a -ah -h2) /h. The last thing I am stuck on is where the +1 in the answer is coming from. Did I miss a step in my simplification?